This invention relates to dinitromethane and to a method for preparing its alkali metal salts. In a more particular aspect, this invention concerns itself with a simplified and economical process that permits the convenient synthesis of alkali metal salts of dinitromethane through the use of methyl malonate and methyl dinitroacetate as reaction components.
Dinitromethane and its salts find wide application as starting materials and key intermediates in the synthesis of gemminal dinitro compounds, polynitro explosives and propellants. The wide utilization of these materials serves to illustrate their importance in chemical synthesis. Unfortunately, the lack of a simple and economical procedure for preparing these key intermediates has limited their use and effectiveness and requires the use of expensive and problematic synthesis for their preparation such as those described hereinafter.
It is known from P. Duden, Ber., 26, 3003 (1893) that free dinitromethane is an unstable pale-yellow oil and decomposes vigorously even at ambient temperatures. The alkali metal salts of dinitromethane, however, are quite stable. The potassium salt was first prepared by the reduction of potassium bromonitromethane with hydrogen sulfide in accordance with the method of R. Villiers, Bull. Soc. Chem. Fr., 41, 281 (1884). More recently, potassium dinitromethane has been prepared by the Ter Meer reaction of chloronitromethane as shown in H. Fener et al, J. Arm. Chem. Soc., 73 1360 (1951). Unfortunately, this reaction only produces yields of about 23 percent. The dinitromethane salts can also be obtained from the alkali salts of dinitroethanal according to the methods shown by P. Noble et al, Chem. Rev., 64 19 (1964).
The alkali salts of dinitromethane have proven to be very useful as starting materials in the synethesis of a gemminal dinitro compounds. For example, potassium dinitromethanal reacts readily with one or two moles of formaldehyde to give potassium dinitronethanol and 2,2-dinitropropanediol, respectively. The fluorination of alkali salts of dinitronethanol, in turn, produce fluorodinitroethanol. Fluorodinitromethane and 4,4-dinitropimelic acid are other gemminal dinito intermediates found to be useful in the synthesis of polynitro explosives and propellants.
From the above examples, it can be seen that dinitromethane salts are important reactant materials which find wide application as key intermediates in a variety of chemical syntheses. Consequently, a considerable research effort has evolved in an attempt to find efficient, economical and practical routes for preparing the alkali salts of dinitromethane. Heretofore, the lack of practical routes necessitated the use of methods based on the Ter Meer method, the use of nitrogen or the oxidative nitration reaction.
Nitroform, used in the synthesis of fluorodinitroethanol, is produced by nitration of acetylene or acetone. Both processes produce large amounts of nitrogen oxides which present expensive pollution problems. In its applications, for the synthesis of gemminal dinitro compounds, one nitro group of nitroform must be removed adding to the cost of this process.
In the oxidative nitration route, gem-dinitro compounds are prepared by reacting mononitro compounds with a mixture of silver nitrate and sodium nitrite. In a large scale production, this method requires a large capital investment in silver nitrate and also suffers from mechanical losses of silver.
The Ter Meer reaction is limited to the synthesis of terminal gem-diniro compounds. As already indicated, the yield of dinitromethane in the Ter Meer method is low. Also, in many cases, nitrohalo starting materials needed in this reaction cannot be obtained in good yields. With the present invention, however, the problems associated with the prior art methods have been overcome by a method of synthesis in which the alkali metal salts of dinitromethane are prepared by nitrating methyl malonate to form methyl dinitroacetate. The dinitroacetate is then reacted with sodium or potassium hydroxide to effect its saponification and resulting production of the corresponding alkali metal salt of dinitromethane. This unique method provides a solution to the problem of finding a practical and economical route for synthesizing these useful intermediate reactants in high yield.